Fifty gifted students have been disqualified from an exam after teachers mistakenly told them they could take books in with them, a school has said.

The year 11 pupils at Kenton School in Newcastle will have to resit their English language and literature AS-levels as a result.

The top-set students, who were sitting the test a year early, were told they could refer to a copy of Anita Shreve's Eden Close during what was actually a closed-book assessment.

On finding out about the blunder, the exam board said it had no choice but to disqualify all 50 candidates, who will have to resit in January.

Kenton School's headteacher David Pearmain said the school, which became an academy in May, was "mortified" by the mistake.

"It was a bad mistake and I have personally apologised to the students affected by it and to their parents," he told Newcastle's Evening Chronicle. "The school very unusually made a mistake and it is a horrible mistake on exam entries."

The students have already completed the first unit of their AS-levels, which will stand. But they cannot be awarded a grade without a mark from the second unit.

In a letter to parents, the school, which has launched an investigation, apologised. It said it would provide extra tuition and arrange the resits in light of the "serious mistake" by the English department.

Awarding body AQA, which organised the exams, said it was contacted about the use of "unauthorised material" and had to disqualify the pupils in the interest of fairness.

A spokeswoman said: "The guidance we provide to schools and colleges is very clear, so issues like this are quite rare. However, if situations like this arise we need to be fair to all students taking our exams. We therefore, unfortunately, have no option but to take this action, but we do so knowing that they have further opportunities to sit this unit."